Composite article and method of making



Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE COMPOSITE ARTICLE ANDMETHOD OF MAKING No Drawing. Application December 24, 1931, Serial No.583,154

14 Claims.

This invention relates to composite articles and methods of making; andit comprises a composite plate, panel or stamped shallow articlecomposed of an impervious, water-resistant integral body of resinderived from formaldehyde and urea in about the molecular proportion of1.5:1, bonded to a contained, integrally united body of open texturedwoven or felted fiber, such as pulp board; and it further comprisespartially neutralizing commercial, somewhat acid formaldehyde solution,dissolving urea. therein in about the proportion of one molecule to 1.5molecule of formaldehyde, maintaining the mixture at a temperaturebetween and 30 C. for four to 15 hours, cooling being used whennecessary, impregnating open textured sheets or articles of wood fiberor the like with the resulting thin liquid in the amount that can beheld by capillarity, drying in a current of air and finally submittingthe dried article to heat and pressure to close the voids and compactthe article, producing an infusible continuous body of resin; thearticle being sometimes flat and sometimes being otherwise shaped whilewet, or during heating, by the use of suitably contoured pressingmembers; all as more fully hereinafter set forth and as claimed.

This application is a continuation in part of my prior applicationSerial No. 494,693. In that application I describe and claim methods ofmaking improved fiber-containing molding compositions offormaldehyde-urea products, adaptable for hot pressing methods, whereinthin mobile liquids or solutions of initial formaldehydre-urea reactionproducts are prepared, absorbent fibrous material is impregnated withsuch liquids and the moist impregnated fiber dried at temperaturesinsufficient to resinify. the formaldehyde-urea reaction products thusproducing molding compositions comprising said fibrous materialsimpregnated with a potential resin. Specifically I have described andclaimed molding powders so made, the dry impregnated material beingground to a powder. In making such molding powders, loose absorbentfibers may be advantageously employed to facilitate the production ofpop-corn like masses easily reducible to a powder by grinding.

The present invention is directed to the manufacture of composite moldedarticles from such molding compositions containing absorbent fibersuniformly impregnated with said potential resins wherein the moldedarticle obtained comprises a continuum of formaldehyde-urea resincontaining a body of felted fiber as a reenforcement thereof. In thepresent processes, a body of felted absorbent fiber, rather than loosefiber, is employed to absorb or take up the said thinly mobile liquids.In this way, more or less preshaped or pre-formed molding blanks can bedirectly obtained; pre-forms which after drying may be converted intothe final molded articles by compacting under suitable heat andpressure, sometimes, even, by mere hot stamping. The heat and pressureshould be sufficient to fuse or soften the potential resin, compact theblank and then resinify the formaldehyde-urea product. While the molarratio of 1.5:1 mentioned ante is advantageous, it may be varied somewhatwithin the range from 1.55:1 to 1.05:1 as disclosed in my said copendingapplication Serial No. 494,693. Any of the thin mobile solutionsprepared by the various methods described in my prior application may behere employed for impregnating sheets or blanks of .felted absorbentfibers as set forth post.

An object attained in the present invention is the provision of asimple, direct and economical way of manufacturing high grade articles,flat or contoured and of neat and decorative appearance, from flat stockby hot pressing or stamping. By high grade articles, I mean those ofmaterial sufficiently impervious and resistant to withstand, as anaccelerated test, the action of boiling water for half an hour. The flatstock is made from urea, formaldehyde and ordinary sulfite pulp board orany other sheeted, open textured, fibrous material, The urea andformaldehyde are combined and used in such a way as to avoid waste ofeither. Scrap and trimmings of fiat stock made in cutting blanks toshape and dimensions are not wasted, being utilized in various ways, asin making molding powder.

Instead of urea, I can use the substituted ureas, such as thiourea,phenylurea, methylurea, etc., but they are more expensive than ordinaryurea and their use offers no great advantage in the present process.Similarly, while other aldehydes, such as acetaldehyde furfural, etc.,and other forms of formaldehyde; such as paraform, etc., can be used inlieu of ordinary 3040 per cent commercial formaldehyde solution, theadvantage is not commensurate with the expense.

Clean urea of the fertilizer grade, commercial formaldehyde and ordinaryone-eighth inch sulfite pulp board are the only materials necessary forsatisfactory operation. No special apparatus is required other than ahot pressing or stamping equipment.

It is possible within thepresent invention to make a laminated fiatstock in continuous operation, traveling webs of paper being treated andassembled to makea stock of any desired thickness; but this, again, isordinarily hardly worth while. I do, however, sometimes in attainingspecial decorative effects, overlay a pulp board base with a decorativelayer of thin paper treated according to this invention.

In the prior art, excellent articles of formaldehyde-urea resins, withor without a filler, have occasionally been produced, but most of theknown methods of manufacture lack certainty of operation. In thepresence of any acid, formaldehyde and urea in aqueous solution reactviolently. Even the slight acidity of commercial formaldehyde, which isoften at a pH of about 3, suffices with warm materials to initiate aselfaccelerating action which brings the liquid to a boil. The resultsvary with conditions. The maximum amount of formaldehyde with which ureawill react is in the molecular proportion 2:1; and in order to restrainthe formation of precipitates or hard gels having a less ratio offormaldehyde, it is the custom to use more formaldehyde than correspondsto 2:1; the proportions being sometimes as high as 4:1. The excess mustbe disposed of in some way prior to producing the final resins.

Many methods of making formaldehyde-urea resins have been proposedlooking toward a greater certainty of operation; but in all cases theinitial reaction between the two bodies is performed in aqueoussolution; the water being afterwards, removed in someway. Chemicalreaction is usually nearly completed in this initial action. In theearliest method, the initial reaction liquid is boiled down, allowed togel and the gel baked to remove residual water and formaldehyde.Sometimes this method gives clear, hard, colorless, glossy resins ofmuch merit; but not always, even with laboratory control of conditions.In other methods, conversion of the reaction products into dry materialswhich can be used in molding powders has been proposed; but thesepropositions have not produced high grade molded articles as a matter offactory routine.

As stated, the initial reaction is always in aqueous solution and evenwhere a precipitate is not produced and the liquid remains glass clear,a result much sought, it is always viscous and gummy. The reaction inaqueous solution has gone too far; there is but little reactivity leftto be utilized in making solid articles. The use of these viscousliquids for coating hats, etc., has been proposed and is practicable,since a thin film exposed to air in time will lose water andformaldehyde and set. But the liquids are too gummy to be used forimpregnating fiber and, as a matter of fact, it is often difllcult toadmix ordinary fillers. These gummy liquids do not really impregnatefiber in the sense that the solids suspended in the liquid enter thecapillaries of the fiber; instead colloidally suspended resinous matteris more or less filtered out merely coating the surface of the fiber.

Part of this gumminess I ascribe to the use of high reactiontemperatures (usually around 100 0.), producing a far going reaction;producing polymerization and formation of colloid suspensions ofresinous formaldehyde-urea products. At all events, I have discoveredthat, by keeping the temperature of a solution of urea in aqueousformaldehyde down within the range of 20 to 30 0., I can effect a slowbut complete reaction of urea, without developing polymerizationsuflicient to make the final liquid product viscous or gummy. The actionis limited to this extent. In fact, using the ordinary 30 to 40 per centcommercial formaldehyde solutions and urea, I can produce reactionliquids which, in spite of a 40 to 50 per cent content of solids, arethin enough to be filtered and which readily enter capillaries. They arenot resinous in character, though the contained solids can be, and are,resinified later. They are therefore well adapted for impregnatingporous materials; a fact which forms the basis of the present inventionsince after entrance they can be polymerized in situ to make aresinified more or less glassy continuum. In obtaining these thinliquids, it is neither necessary nor desirable to use the ordinary highformaldehyde ratios,.2:l, or more. In fact, I can and do use a ratio of1.511 in making the initial liquid product, since this ratio I findhighly desirable in the final finished resins to be prepared from it.With this ratio, the final resins constituting the bond or continuum ofthe heat-treated article, can be made containing neither free urea norfree formaldehyde and having a maximum of stability. And there is noquestion of adding too much formaldehyde in the beginning and thengetting rid of the excess; a stumbling block in the art.

In securing the slow, regular, gentle and complete but limited action Idesire, acidity must be controlled within certain limits. In theordinary methods, the presence of an excess of formaldehyde restrainsthe ac ion of acid to a large extent; and without this excess,regulation of acidity becomes important. Commercial formaldehyde usuallycontains enough formic acid to give it a pH of 3 and at this or anygreater acidity, with warm formaldehyde solution containing dissolvedurea, the reaction tends to become violent and self-accelerating; theliquid generally goes to a boiling temperature. In the absence of moreformaldehyde than corresponds to a-2:1

ratio, the boiling mixture may set to a hard spongy solid or deposit aprecipitate, according to conditions. This is one of the reasons for thegeneral use of high formaldehyde ratios.

In using the 1.521 ratio, I find that with an acidity near the neutralpoint, say pH 6.4, no violent action takes place in the temperaturerange 20' to C. and the mixture heats only slightly. But action takes along time; 10 to 15 hours usually.- With such an acidity, it is oftenconvenient to let the mixture stand over night. At an acidity of pH 6with a mixture at room temperature, reaction is somewhat quicker andmore than slight cooling is seldom' required. At pH 5 cooling is used inthe first hour or so of action operating at ordinary room temperatures.At pH 4 careful control of the temperature is needed and energeticchilling is generally necessary to rapidly dissipate heat from thereaction.

Commercial formaldehyde solution is, as stated, around pH 3 and I findit ordinarily necessary to partially neutralize it. Without this partialneutralization, reaction and development of heat become lnconvenientlyrapid. In neutralization, I usually employ triethanolamine; but anyconvenient base, such as soda, potash, lime, etc., can be used. In thesmall amount required to change the pH value, the particularneutralizing agent used is not vital.

In dissolving, urea exercises an energetic chilling action and in makinglarge batches by adding urea to formaldehyde solution, the temperaturemay go down nearly to zero centigrade. In making up such a batch, it isusually warmed somewhat; enough to bring it back to room temperature.After this, it is let alone or cooled, according to the pH value of theformaldehyde. In any case, care is taken that the temperature does notgo above 35 C. until reaction is over. A temperature above 35 C. givesgreater viscosity than is desired in the present invention; and atemperature kept between 25 and 30 C. at all times prior to completionof the reaction in aqueous solution, gives the best mobility.

The progress of the reaction may be followed by testing for freeformaldehyde in any of the usual ways. When the aldehyde content ceasesto diminish the liquid is still thin and mobile and is ready for use asan impregnant. In the present invention this liquid is generallydirectly taken up in a body of open texture woven or felted fiber suchas pulp board; and is then dried in place. Drying is at a lowtemperature and the initial reaction in the aqueous solution does not goforward beyond a certain point; the course of reaction is, so to speak,arrested by the drying. When the dried board is subjected to heat andpressure reaction is completed. Polymerization and other changes occurwhich produce a solid resinous continuum. The water soluble solids inthe thin liquids are not resinous; they are at most potential resins.Instead of using the initial thin liquid directly as an impregnant itmay be spray dried to give a dry soluble preparation; a solution ofwhich can be used in the same way as the initial liquid.

On gradually heating'the dry solid preparation, either that made byspray drying or that contained in the pores of the pulp board, etc., itsoftens and becomes plastic and then flows to shape. This thermoplasticproduct at a temperature around 120 sets to a hard, infusible, insolubleglassy resin of perfectly permanent character. The setting is alwayscomparatively quick, but becomes much quicker in the presence of aciditygreater than pH 6. With slow heating in the open air, degenerativechanges may take place and the resin is not so good; but heating underpressure with the ordinary molding technique, good results are secured.

As will be noted, reaction is in two stages, a

' first stage where bodies are formed giving a thin mobile aqueousliquid without substantial polymerization and a second stage, after thewater is removed, where reaction is completed; where polymerization isproduced and resins result.

'The greater the acidity of the liquid, the-easier is the drying ofporous preparations containing it and the quicker is the setting orcuring of the dry product under heat in forming the final resins.Sometimes, this quicker setting is wanted and sometimes not.

Using commercial formaldehyde solutions of 30 to 40 percentconcentration and the amount of urea necessary to give the stated 1.5:1ratio, the thin liquid formed after completion of reaction is quiteconcentrated. It runs 40 to 60 per cent total solids. In any utilizationof the liquid product, it is necessary to remove the water withsubstantial completeness before it becomes gummy and thick. As stated,this can be done by spray-drying, but in the present invention, it isordinarily done, as stated, in another way: by taking up the liquid witha sheet or article of paper pulp and drying the impregnated pulp in acurrent of air. The air may be warm, but the temperature of the materialbeing dried should not go over C. In another and copending application,Serial No. 494,693, wherewith the present application contains certainmatter in common, I have described and claimed the production of amolding powder utilizing the facts as so far recited. In this copendingapplication, loose paper pulp fiber is saturated with the thin liquid inthe amount which it will hold without dripping and is then dried in acurrent of air to give loose agglomerated material. This is recomminutedto form a molding powder which can be set under heat and pressure;pressure being used of the order of 2000 pounds and the settingtemperature being around C.

' In the present methods I may utilize any of about 4 inch thickness isa convenient material.

This paper board I saturate with the thin liquid and dry as before.Shapes may be cut from the pulp before impregnation or after drying.

In making panels and stamped articles, pulp board may be cut to theright dimensions, impregnated and roughly contoured while wet. The wetarticles are dried, as stated, in a current of air and are then hotpressed under such pressure as may be deemed desirable, but at atemperature rising to 120 C. Shape may be given in. the pressing bysuitably contouring the press head. It is convenient to rough shapearticles while the pulp is wet and complete the shaping in the hotpressing.

Under the influence of heat and pressure, the solid condensationproducts of the dried solution fuse and fill the voids and thenpolymerize to form infusible, insoluble material. These actions aresuccessive and while the total time required is very short with ordinarymold pres sures there is sufiicient flow to fill the mold prior to thesettingstage. Articles made under the present invention withstand 30minutes exposure to boiling water without damage. Thus in the presentmethods I produce hot pressed articles which primarily differ from thoseobtained in my acknowledged prior processes in that here the the feltedfiber serves as a reenforcement for the resin continuum formed in situ,in and on the fibres, during the hot pressing. In some cases the hotpressing is substantially a compacting and Welding of the pre-shapedimpregnated composition, the filtered fibers retaining their originalmutual relation to each other.

In hot pressing thick articles, a slightly longer time is required togive penetration of heat; and for relatively thick articles, a pH of 6.4in the original reaction is best. For thinner sheets, a pH of 6 or even5.5 gives a quick setting and also a quicker drying.

The liquid reaction product may be dyed by any convenient dye notaffected by formaldehyde. The solution being white and colorless, truecolors may be obtained.- With a good grade of clean ur'ea, filtration ofthe solution is not terial.

ordinarily necessary for the present purposes. If, however, for anyreason a glass clear solution is wanted, the reaction product may befiltered in the ordinary ways and by ordinary means. With dirty urea,sometimes it is desirable to filter before effecting reaction.

Where sheeted fiber is impregnated and dried before cutting out shapes,the scrap and trimmings are useful in producing the molding powder of mycopending application. In so doing, I comminute the scrap to furnish afine powder and, ordinarily, at this time introduce something whichwill'produce a little acid in the mold and give quicker setting.Phthalic acid resins containing an excess of phthalic anhydrid in solidsolution, betabromhydrocinnamic acid, benzoyl peroxid, etc., are usefulfor this purpose. Some zinc stearate as a lubricant is also a usefuladdition. Or, impregnated scrap may be repulped, shaped, redried and hotpressed.

Where the shapes are first cut and then impregnated, the scrap ofunimpregnated paper board may be used to furnish fiber for makingmolding powder according to my copending application.

In a specific embodiment of the present invention making a white fiat 4x 5 panel for a scale housing, commercial inch sulfite pulp board is cutto size and the 4 x 5 sheets dipped in an impregnating bath, removed andallowed to drain. This bath is made by dissolving 320 pounds of urea in650 pounds of 3'7 per cent formaldehyde solution brought to 6.4 pH withtriethanolamine. The cold solution is warmed to 25 C. and allowed tostand over night before use. This solution used with pulp board in theamount which will be held by capillarity will give about 60 per centresin and 40 per cent fiber in the final hot pressed article.

The drained impregnated panels are next dried in a current of hot orwarm air, care being taken to avoid a temperature over C. in the ma- Airat that or a less temperature should be used in finishing the drying,when the evolution of water vaporsl-ackens.

The dried panels are then hot pressed, using a press head heated to C.and a pressing time of seconds. Under the heat and pressure, the

reaction product softens or liquefies and flows,

allowing complete obliteration of voids, and then sets to a hard,glassy, infusible, insoluble, permanent resin. With white fiber andundyed impregnant, the general appearance of the panel is that of whiteporcelain; a surface film of transparent resin giving the efiect of aglaze. Handsome tableware may be made by impregnating good qualitycommercial pulphoard plates and saucers, drying and hot pressing.

The felted relation of the fibers in pulpboarcl has a double function inthe present invention. In the drying stage, the open texture which ismuch like that of blotting paper, permits the absorbed liquid to presenta relatively enormous .total film area to freely entering air, givingrapid and complete drying. The better the drying the better the resultsin hot pressing. In the pressed article, the felted fibers preservetheir original relation and original length, giving an unusuallyeflective reinforcement against strains from any direction. Theincorporated body of fibers gives articles underthe present invention arugged nature; making them proof against cracking and shattering.Mechanically, they are high grade.

What I claim is:

1. In the manufacture of improved stable pressure-shaped heat-set moldedarticles resistant to boiling water and to shock, having the appearanceof glazed porcelain and composed of a resin continuum containing areenforcing body of pre-.

felted fiber, the improved process which comprises hot pressing asubstantially dry molding composition comprising a felted body of paperpulp uniformly impregnated and saturated with an arrested initialreaction product of formaldehyde and urea, to produce said moldedarticle, said body of paper pulp being a preshaped and formed body, saidarrested initial reaction product being a potential resin havingformaldehyde and urea residues combined in a molar ratio between 1.05:1and 1.55:1, being an arrested, low temperature, acid-condensed initialreaction product of formaldehyde and urea in said ratio, being soluble,fusible and substantially free of volatiles, and said potential resinfurther being capable of heat hardening without substantial liberationof volatiles at temperatures around 140 C. and being in said moldingcomposition capable, when under a temperature around 140 C. and apressure of one ton per square inch, of flowing sufficiently to becomecompacted and dense prior to heat setting, said molded article beingresistant to the action of boiling water for one-half hour withoutdeterioration.

.2. The process of claim 1 wherein said potential resin and the resinformed from it have formaldehyde and urea residues fixedly combined in amolar ratio of 1.5:1.

3. In the manufacture of porcelain-like articles resistant to shock andto boiling water, the improved process which comprises preparing anunheated, partially neutralized solution of formaldehyde and urea inabout the molecular proportions 1.5:1, allowing the mixture to stand inan unheated state for reaction to take place until the urea is combinedand until a thin mobile solution free of gumminess is obtained,impregnating an article of felted fiber with such slightly acid solutionprior to the development of resinous character therein, drawing offexcess solution, drying the slightly acid impregnated article at lowtemperatures insufficient to resinify the formaldehyde-urea reactionproduct and hot pressing to produce an integral body of heat-hardenedresin containing the fiber.

4. As an improvement in the manufacture of shaped, hardened and rigidarticles from urea tured shaped mass of felted fibers with sufllcient ofsaid mobile solution of reaction product to associate a. substantialamount of non-resinous urea-formaldehyde reaction products with and intosaid fibers, drying the impregnated mass at temperatures not exceeding80 C. to secure a dryness sufficient to enable the dry mass to be hotpressed without veslculating and, finally, hot pressing the dry mass tocompact it and to fuse and resinify the urea-formaldehyde product into acontinuum wherein the molar ratio of formaldehyde tourea persists,

5. In the manufacture of shaped, heat-hardened articles, having acontinuum of stable resistant formaldehyde-urea resin reenforced with abody of pre-felted fiber impregnated and. bonded with said resin, theimproved process which comprises impregnating a pre-formed, preshaped,felted body of fiber with a thin mobile liquid capable of enteringcapillaries, said liquid comprising a slightly acid aqueous solutionhaving an acidity less than that corresponding to pH 3 and containingdissolved therein a non-resinous formaldehyde reaction product, themolar ratio of formaldehyde to urea being 1.5:1, drying the impregnatedbody thus obtained in a current of warm air until substantially free ofvolatiles to produce a fusible heat-hardening formaldehydeureacondensation product having formaldehyde combined with urea in a molarratio of 15:1, and then molding the dried impregnated body thusobtained, undersuificient heat and pressure to produce the final shapedarticle and to fiow and heat-harden the formaldehyde-urea product into acontinuum of stable, infusible resin, thus forming an integral body ofresin containing the felted fiber.

6. In the manufacture of shaped, heat-hardened articles, having acontinuum of stable resistant formaldehyde-urea resin reenforced with abody of prefelted fiber impregnated and bonded with said resin, theimproved process which comprises impregnating an open-textured feltedbody of fiber with a thin mobile, non-gummy liquid capable of enteringcapillaries, said liquid being a slightly acid aqueous solution havingan acidity not greater than pH 4 and containing dissolved therein anon-resinous formaldehyde-urea reac-./ tion product, the molar ratio offormaldehyde to urea being 1.5:1, shaping the moist impregnated bodythus obtained to give a roughly shaped article, drying the roughlyshaped article thus formed, at a low temperature, said temperature beingsufficient to remove volatile substances without resinifying theformaldehyde-urea product and then compacting the dried volatile-freebody impregnated with a fusible heat-hardening formaldehyde-ureacondensation product so obtained, under heat and pressure, the heat andpressure during pressing being sufficient to fiow and then resinify thesaid fusible condensation product.

7. In the manufacture of stable, pressureshaped, heat-set shapedarticles having a continuum of stable, resistant, formaldehyde-urearesin reenforced with a body of pre-felted fiber impregnated and. bondedwith said resin, the steps which comprise mixing together formaldehydeand urea in slightly acid solution, the molecular proportion offormaldehyde to urea being between 1.05:1 and 1.55:1 and the acidity ofthe mixture being between 5 and 6 pH, maintaining the mixture at arelatively low temperature not exceeding 35 C. until all the urea hascombined with formaldehyde and a thin mobile solution capable ofentering capillaries and containing an initial water-soluble reactionproduct is formed,

impregnating a pre-felted body of absorbent fibrous filler with the thinmobile non-gummy solution so obtained, to form a moist impregnated,pre-felted fibrous body, and then arresting the reaction short of theresinous stage, by evaporating off the contained water from the slightlyacid moist body so produced, at a temperature not exceeding 80 C. torecover a dry body of pre-felted fiber, impregnated with a potentialresin having formaldehyde combined with urea in said ratios and capableof being molded under heat and pressure at a temperature of 140 C. and apressure of 1 ton per square inch without substantial liberation ofvolatiles sufllcient to cause vesiculation and blistering.

8. The process of claim '7 wherein the said dry body of pro-felted fiberimpregnated with said potential resin, is hot pressed to produce thefinal shaping and to resinify the potential resin in situ, subsequent tosaid shaping, the temperature and pressure being suflicient to soften,fiow and heat-harden the said potential resin in that order, convertingit into an insoluble, infusible, sound, stable, resistant resinous body.

9. An improved stable molded article resistant to boiling water and toshock and having the appearance of glazed porcelain, said. article beinga pressure-shaped, heat-set product comprising as a continuum, animpervious integral body of stable, resistant formaldehyde-urea resincontaining a reenforcing body of pre-felted fiber, said molded articlebeing resistant to the action of boiling water for one-half hour withoutdeterioration, said felted fiber being uniformly impregnated with andbonded together by said resin continuum and serving as a substantialreenforcement thereof, and said resin being insoluble and infusible andhaving formaldehyde combined with urea in a molar ratio between 1.55:1and 1.05:1, with all the formaldehyde fixedly combined therewith.

10. The product of claim 9 wherein said ratio of formaldehyde to urea is1.511.

11. The product of claim 9 wherein said molded article is a dish fortable use.

12. The product of claim 9 wherein said molded article is a panel forhousing apparatus.

13. The article of claim 9 wherein said prefelted fiber is uniformlydistributed throughout said resin continuum and is itself asubstantially continuous reenforcement.

14. The article of claim 9 wherein the felted fibers of said pre-feltedbody thereof have substantially their original mutual relation to eachother as in the pre-shaped molding composition and the proportion ofsaid reenforcement to-said resin continuum is substantially the same atall points in the said molded article.

ARTHUR M. HOWALD.

